Problem with Plywood

So I built a window seat using birch ply from a big box store and when I started sanding it with 150 grit paper I got a few areas like this where the top veneer started peeling away. I pretty much stopped sanding to prevent further damage and was going to leave it as is because we are putting a cushion on the bench that will cover this but after priming I decided it was going to bother me if I didn’t fix it. Does anyone have any recommendations for filling these areas in and smoothing it out? Looking for something fairly easy and quick if possible.